It is common practice among utility companies and the like to store coal in substantial quantities at a power plant, and also to stockpile coal at sites remote from the power plant for later use in the event of a coal strike or shortage. Such coal piles may be on the order of seventy feet high and cover several acres of land. In active piles at a utility site, coal is often added to and extracted from the central portion of the pile, while the sides may remain substantially untouched for long periods of time. Stockpiled coal may remain dormant for months at a time.
A number of problems have long plagued utility companies and other coal users in connection with coal storage piles. For example, the wind may carry coal dust from the pile surface for a substantial distance and cause undesirable side effects to the surrounding environment. Similarly, rain may wash or erode the sides of the coal pile. An additional problem, particularly during the summer months, is the hazard of spontaneous combustion at the surface of the coal pile, which may spread to a smoldering fire within the pile itself which is difficult to extinguish.
It is common practice among utility companies, particularly during the summer months, to spray water over the surface of the coal pile to cool the surface and wet down the surface dust against wind and other forms of erosion. However, the water either filters through the interstices in the coal pile or evaporates quickly from the pile surface, so that wetting of the pile surface provides at best only temporary alleviation of the problem.